1.) 56 cm Cannondale Evo.
2.) Zipp SL70 w/ 110mm -17 stem. Slammed.
3.) Drafting huge truck at >40mph for fun, coming out of the draft things got dicey for some reason.

Had been a while since I'd gotten a speed wobble; had almost forgotten how nasty it could be.

1. Giant Trinity composite Lg
2. Giant brand Aero pad set up, many spacers under the stem (8cm maybe), Zipp vuka bull base bar (this has since been remedied).
3. Descent on the LPlacid course, think my flexy Carbon wheels (old style Boyd) flexed on rough pavement, nicked frame, and then bike got all squirrelly with speed wobbles...going 40+mph

to me, when i say or hear speed wobble, it's not a 1-time thing with a bike. it's a particular characteristic of that bike, that bike's parts, maybe that bike's rider. it's just like a shimmy in your car, where it might start at a certain speed and then stop at a higher speed. at a particular point, the bike starts to oscillate, just like the wheels in your car during a front-end shimmy. it's very unnerving.

sometimes it happens in a freak situation, on a long descent, you're cold, you get "sewing-machine leg," and that is the agent that starts the wobble. but usually you don't get it once only.

is this what you experienced? or was it a very disconcerting buffeting from the truck once you left the draft?

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Dan Empfield
aka Slowman

You flew through his jet stream? Hasn't Goose's death taught you anything?

1) Cervelo P5-6 54cm
2) P5-6 config with 10mm spacer and the low profile setup.
3) Slight down hill at 41mph. Roads were fine. Not wet or ice. No wind.

I suspect my 2008 Zipp 404's though. They have seen their better days. The tires are GP 4000s. Front is fine, no major flaws, rear has a slight flat spot on it from the trainer.

Not the first time getting speed wobble with these 404's and on different bikes. Looking forward to new Flo 60/90.

I'm familiar with what you meant by speed wobbles. Used to call them "death wobbles" on skateboards that were the same sort of thing and I used to get a particular speed wobble on an older bike down a steep descent with some consistency.

Something about the speed I was at combined with the airflow coming out of the draft (and possibly my position at the time?) made the bike go into that same classic speed wobble, where it was starting to oscillate and had the feel it was about to go out of control. It lasted significantly longer (or at least felt like it did) than just the initial wake of leaving the truck. Tried de-weighting the saddle and that seemed to correct things enough that I slowed and kept it under control.

Reminded me a little of the video I've seen where the wobble could be induced by banging the handle bars. Perhaps coming out of the draft was a little like that.

was it the only time you experienced it with this bike? when did it stop? only when you slowed down?

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Dan Empfield
aka Slowman

Ha, nice! Like Mav, I have a need for speed even if it sometimes isn't the smartest thing in the world. So fun right up until I thought I was going to die.

So far the only time, I don't think I usually get up to that speed on this bike, so not sure if it is the characteristic frequency of this bike to have issues at that speed yet and I'm not excited to do more experiments along those lines. It stopped as I stood up a bit off the saddle and slowed down. Pretty sure it was still happening well after the major wake of the truck was gone, so I think the truck wake initiated it and wasn't what was keeping it going.

Also, check the wheel dish. Especially, 11 speed rear-wheel dish.

Cheers,

G

Based on my experience, I think there's at least one more bit of information you might want to ask for...

1. 2011 Madone 6.2, 58cm H1 geometry
2. 110mm x -7deg Bontrager RXXXL stem, 42cm Syntace carbon bars, 15mm of spacers
3. transitioning from hoods to tops near the stem (aero tuck for a descent)
4. what else was on my bike: a chunk of steel equivalent to a fully loaded 2-pack (e.g. equivalent mass of a pair of full 28oz bottles and all the stuff triathletes would probably carry in the storage compartment), cantilevered out behind the saddle as part of ride evaluation of the 2-pack attachment hardware

#4 is important. The bike went into speed wobble almost instantly when I removed one of my hands from the hoods early in the descent. The same bike, sans the simulator, has never speed wobbled with or without hand movement in any other condition at speeds in excess of 55mph.

So of course I went out and experimented some more a couple weeks later. Same load (preproduction prototype 2-pack this time, fully loaded) installed on 2014 9srs and 7srs SCs with multiple wheelset combinations (including Aeolus D3 9's, old Aeolus 5.0, old RXXXL tubie, Aeolus disk rear, H3 tubie front, etc) and I experienced zero speed wobble at speeds approaching 50mph with random crosswind gusts in the range of 10-15mph. Ran same course, same day, at same speed(s) with the aforementioned Madone on a pair of A9's with and without 2-pack and once again got near instant wobble when it was on and rock solid when it was off.

Yeah, sometimes I'm a guinea pig. I love my job.

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Carl Matson

sounds like an experience in extreme turbulence rather than speed wobble caused by exciting the natural frequency of the bike frame.

Only ever happened to me when I was about 9 on my Raleigh Mini Burner. When my sister found me on the road she thought I was dead..!

But, reason for posting is this is a great opportunity to share a youtube video posted by a certain "drinard" ...
https://www.youtube.com/watch?v=xODNzyUbIHo

Didn't think about the single bottle off the back of my saddle. Maybe it was the position and weight of the bottle for me. It was sitting rather far back, hard for me to reach.

Are we talking a normal slight wiggle... or a full on severe head shake? Under braking? Mid-corner bumps? crosswinds? aerobars? sitting up? How upright. Sometimes have less weight on the front and make it much worse I think.

I've had some shakes, but overall consider them normal and expected in certain conditions.

I've even had loose headset bearing and loose front and real wheel bearing and never noticed anything unusual. I'm also very relaxed on the bars at high speeds. That's the key. You should always "guide" the bike, and use counter steering and pedal weighting, never, ever "steer" anything with 2 wheels above about 5-8mph.

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TrainingBible Coaching
http://www.trainingbible.com

Felt DA4 56
2nd shortest little stubby stem cocked up about 45 deg angle
downhill ~40mph - in aerobars. Pretty sure it was the worn out front tire - pulled from back, so squared off pretty well. Never happened again once I got new tires.

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Proud member of FISHTWITCH: doing a bit more than fish exercise now.

1) Canyon Aeroad 2013 Model - Size XL
2) Stem 100mm, Handlebarwidth 44mm, 1cm spacer.
3) Heading down Ou Kaapse Weg in Muizenberg, with speeds of 82km/h. Was not supermooth tarmac. Just suddenly felt like my front part of the bike started to wobble, and thought I had a flat. Initial reaction was to brake slowly, as I could not look down properly, and it was my first ever speed wooble. Felt like the bike was going to collapse under me, a horrendous feeling. Finally got slow enough to, and my next reaction was to unclip so that I could have my legs out for balance. Felt like the right thing to do. Did notice that if I Pressed the brakes to hard, that the wobble got worse. Eventually rolled to a complete stop, and felt like throwing up. Ever since then I have struggled to do high speed descents again, which probably comes down to a mental issue. And did sell the bike a month after, as I did not trust it anymore.

Cyclist who was behind me said he thought I was going to a a complete wipeout, and he saw steam coming off my wheels at the back, which was probably from me breaking, and the road being a little damp in the morning, although it was like 25degrees celcius.

Have worked my way through three roadbikes (Parlee Z5SLI, Trek 4.3) since then, and only now I have finally found a bike a C60 that I trust for a fast descend!

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My Blog - My Tweets - My Strava
My Bikes - CF SLX, 622SLX, O-1.0, AL9.0, 4.3Disc, Slice BI, C60

interesting. tell me what you think about mass above the ground, distant from the center of mass, and its contribution to speed wobble.

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Dan Empfield
aka Slowman

PS where I work we have a 1200+ ft broadcast tower, which is a replacement for the mast that went before it which was about the same height. It was a cylindrical structure supported by stay wires under high tension. It had been standing for decades. The structure, stay wires and anchors were inspected and oiled regularly and meticulously. And then one day it fell over. The analysis showed that a very specific and sustained wind speed from a particular direction could cause oscillations of a particular frequency, which in turn could cause a standing wave to be set up on one of the stay wires, if the wavelength of the oscillation had a particular relationship with the length of the cable. And when it finally went ping and detached itself the whole bloody thing was pulled over by the tension of the other wires. And Yorkshire didn't have any TV for a long time...!

A cable is a simple object and when considering its length you are talking about nice and simple limited degrees of freedom. Any object can have a natural frequency that it likes to vibrate at, and multiple resonant frequencies when you consider all of the degrees of freedom and then the harmonics. When you consider the structures and sub structures that make up a bike, who bloody knows what conditions could make a bike go wobbly!

Good luck!

I think I don't know too much more than what I experienced. Moreover, I'm not a dynamics guy, so I'm sure what follows will imperfectly sketch out my theory. (paging epic-O!) I theorize that cantilevering a bunch of mass off of a "corner" of this system of (damped) springs that is a bicycle and rider has a higher probability to excite the springs than if it were contained in, say, the main triangle. The further you are from the fixed or contact points, the more bounce...like a diving board. That I was fine until I removed my hand(s) from the bar, and that by doing so I was briefly but significantly changing the system stiffness & damping, seem to mesh with the conventional wisdom on what induces and reduces (once initiated) speed wobble.

Came across this somewhat similar (conceptually anyway) scenario on a recumbent forum.

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Carl Matson

I know exactly what you are asking. (Google Jeep Wrangler death wobble. Oy!) I've never experienced it on a bike. Sideways forces due to crosswind with deep carbon wheels sure. We know what that is and how to deal with it.

1) Cervelo 2010 P2, 56cm
2) 110 stem, slammed, Vision bars, Zipp 404 tubulars
3) Hill decent during a race, started at about 35 mph.

I added counter weights to off set the valve extender weight on my Zipps and never experienced the wobble again.

Never had a speed wobble in 25 years of riding Carbon bikes (first carbon bike was a Kestrel 4000). I have had speed wobbles on Columbus SLX tubed steel bikes at ~ 70-80 kph (in cross winds), but nothing that changing the harmonic by taking my two knees and clamping them together to the top tube did not resolve....just changed the fundamental harmonic frequency of the bike by doing that.

Great Timing...

2014 Speed Concept. Rear bottle setup. Somehow my fit got really screwed up and I was extremely too far forward on the bike from the saddle to my aero bars. I experienced a severe speed wobble every time I went down hill and in excess of 30 mph with my hand position being in the bull horns. It happened 6 times in two days of riding. Needless to say I scheduled a new fit immediately and they moved my saddle back and got a mid-far stem to replace the low-far stem. So far the speed wobble has disappeared but those two days of riding were pretty scary.